Air cell including zinc anode and alkali zincate electrolyte



y 1953 EIICHI SAKAGAMI ET AL 3,392,057

AIR CELL INCLUDING ZINC ANQDE AND ALKALI ZINCATE ELECTROLYTE Filed Aug.19, 1965 Sheets-Sheet :3

Fig. 3

400 400 43% KzZnOz 0 I00 KzZnOe v0 43 KOH I00 75 50 a5 0 KOH you! Ratioof vo/wne Fig. 5

y 1968 aucn-u SAKAGAMI ET 3,

AIR CELL INCLUDING ZINC ANODE AND ALKALI ZINCATE ELECTROLYTE 5Sheets-Sheet 3 Filed Aug. 19, 1963 y 1968 EIICHI SAKAGAMI ET AL3,392,057

AIR CELL INCLUDING ZINC ANODE AND ALKALI ZINCATE ELECTROLYTE Filed Aug.19, 1963 5 Sheets-Sheet 4 22 24 Fig. 8

Load (V) Capacity (AH) Fig. 10 zsol I00 Q \l 43% KzfirOz 0 v 25 5F 75I00 KzZnQ W13 43XKOH m 75 50 5 0 K0 vol y 1958 EIICHI SAKAGAMI E AL 3, I

AIR CELL INCLUDING ZINC ANODE. AND ALKALI ZINCATE ELECTROLYTE Filed Aug.19, 1963 5 Sheets-Sheet 5 United States Patent 3,392,057 AIR CELLINCLUDING ZINC ANODE AND ALKALI ZINCATE ELECTROLYTE Eiichi Sakagami,Kobe, Masao Ozaki, Moriguchi-shi,

Fukutaro Mizukami, Osaka, Jun Watanabe, Amagasakishi, Tomizo Shiramoto,Osaka, Naohiro Furukawa and Rikio Iida, Moriguchi-shi, and KazumitsuJibiki, Hirakata-shi, Japan, assignors t0 Matsushita Electric IndustrialCo., Ltd., Osaka, Japan, a corporation of Japan Continuation-impart ofapplications Ser. No. 820,797

and Ser. No. 820, 798, June 16, 1959. This application Aug. 19, 1963,Ser. No. 303,034

8 Claims. (Cl. 13686) This application is a continuation-in-part ofco-pending application Ser. No. 820,798, filed June 16, 1959 and Ser.No. 820,797, filed June 16, 1959; both are now abandoned.

This invention relates to a new air cell, and more particularly to anair cell wherein the anode, cathode and electrolyte are active carbon,porous zinc made of zinc powder and a 35 to 45 percent solution ofalkali zincate, respectively, the reaction of the said air cell being;

Air cells are known wherein the anode, the cathode and the electrolyteare cast zinc, active carbon and a solution of caustic sodarespectively. The electromotive reaction of such cell is given by thefollowing equation:

Theoretically, this cell requires 1.22 g. of zinc and 1.49 g. of causticsoda per one ampere hour, but practically it consumes much more, namely2 g. (0.28 cc. by volume) of zinc and 1.4-1.6 g. (7-8 cc. of 20 percentNaOH solution) of caustic soda. Consequently, the electrolyte occupies aprohibitively large volume of the cell. Thus, the discharge capacity perone cubic centimeter of the cell volume is 7 10- ah./cm. and thedischarge capacity per one cc. of the electrolyte solution is 0.12ah./cc. and it is impossible to have a larger space efiiciency thanthese values under the condition necessary for the above indicatedreaction. If large capacity is required, the cell volume must be madelarger.

In order to overcome the above disadvantage, it has been proposed toreduce the amount of caustic soda, but in this case a dense oxidizedfilm is formed on the surface of cast zinc, which renders the zincimpassive. This reduces the efiiciency of zinc utilization andaccordingly fails to obtain a cell of good performance.

For the purpose of removing the above drawback, a porous zinc,compression-molded from zinc powder, was proposed for the anode.

In this case, the porosity of zinc anode makes the contact surface ofreaction so large that even if a compact zinc oxide film is formed, itdoes not grow to such a great thickness as to decrease the passing ofelectric current. Thus it is now possible to bring most of the zinc intoan effective electromotive reaction and the defect of the passive stateis obviated. However, the increased efficiency of zinc utilizationinduces the following other drawback.

As the electrolyte of caustic soda solution is consumed and deterioratedprogressively because of the electrornotive reaction shown in Equation1, both the concentration and the amount of the electrolyte decrease.This results in an increase in the concentration of sodium zincate insolution, thereby causing the discharge voltage to decrease. When thecaustic soda is consumed completely leaving unreacted zinc, theelectromotive reaction takes the following form:

Thereafter, consumption of electrolyte and change in concentration ceaseand the reaction shifts to zinc oxide formation at the anode. Thereforethe electromotive reacm 3,392,057 1C6 Patented July 9, 1968 tionconsists of two reactions and discharge voltage changes suddenly at thetransition point which causes a shift of electromotive force as shown inEquations 1 and 2. Even when the reaction proceeds according to Equation1, gradual consumption and deterioration of electrolyte results with aconsequent reduction in activity and lowering of discharge voltage.These disadvantages are drawbacks in this method.

In the method of this invention, of the essential factors of cellconstruction i.e. the anode, the cathode and the electrolyte, only theanode is made of material which is consumed and deteriorated by thereaction, while the other two are made of materials which are notconsumed or deteriorated by the reaction.

The object of this invention is thus to .provide an air cell which has alarge capacity but small size and minimized weight, i.e., an air cellhaving high volume efiiciency and high weight efficiency.

Another object of this invention is to provide an air cell having asmooth and constant discharge characteristic.

Another object of this invention is to provide an air cell having lowself-consumption.

Still another object of this invention is to provide an air cell whichis easy to handle and maintain, and is superior in heat-resistant,cold-resistant and humidity-resistant properties.

In the accompanying drawings, FIGURE 1 is a planview of AWZ-26O type airwet cell, one embodiment of an air cell of this invention, FIGURE 2 is across-section view along the line A-A of FIGURE 1, FIGURE 3 is thecharacteristic curve of continuous discharge of this air wet cell at 20C. and ma., FIGURE 4 is the characteristic curve of intermittentdischarge for 4 minutes after stoppage of 56 minutes in this air wetcell at room temperature and 509, FIGURE 5 is the characteristic curveof continuous discharge at 20 C. and 200 ma. in various concentrationsof K ZnO of this air wet cell, FIGURE 6 is the curve which shows therelation between K ZnO concentration and capacity of this air wet cell,FIGURE 7 is the characteristic curve of continuous discharge at 20 C.and 200 ma. when the conventional electrolyte solution is used in theair wet cell, FIGURE 8 is the side sectional-view of another type of airdry cell embodying a feature of this invention, FIGURE 9 is thecharacteristic curve of continuous discharge of this air cell at 20 C.and 20 ma., FIGURE 10 is the characteristic curve of intermittentdischarge for 4 hours after stoppage for 20 hours at 8 ma. in this aircell, FIGURE 11 is the characteristic curve of continuous discharge at20 C. and 20 ma. in this air dry cell, FIGURE 12 is the curve whichshows the relation between K ZnO concentration and capacity of this airdry cell, and FIGURE 13 is the discharge curve at 20 and 20 ma. when theconventional electrolyte is used. FIG. 14 shows curves of capacity tovolume of an electrolyte when 200 g. of Zinc are used for the anode ofan AWZ260 type air cell, in which curve No. 27 uses as electrolyte a 43%aqueous K ZnO solution, No. 28 a 43% aqueous K ZnO solution containingCa(OH) to inhibit denaturation of KOH owing to CO in air and No. 29 a43% aqueous KOH solution.

In the cell of this invention, the reaction of the electrodes is:

this invention does not participate in the elect-romotive reaction.Accordingly there is no consumptlon of elec- As electrolyte, an aqueoussolution of alkali zincate such as sodium zincate or potassium zincateis used. Though a concentration of from 35 to 40 percent by weight ispreferable as shown in FIGURES 6 and 12, a concentration of 43 percentby weight is most preferred.

Alkali zincate undergoes the following hydrolysis reaction 3:

It was discovered by the present inventor that so long as theconcentration of alkali zincate is in the range of 3050 percent (byweight), 87 percent (by weight) of alkali zincate in solution does notundergo hydrolysis, i.e. only 13 percent (by weight) of alkali zincateundergoes hydrolysis and at this point equilibrium is established in theaqueous solution.

Consequently in a 3545 percent (by weight) aqueous solution of alkalizincate, there exists very small quantity of hydroxyl ion whichmaintains the equilibrium of hydrolysis. When the cell is constructedwith this electrolyte, the reaction shown in Equation 1 does not occurbut reaction 2 proceeds smoothly, at all times, without variation inconcentration and without consumption of electrolyte.

A 43 percent aqueous solution of potassium zincate is made, for example,by dissolving 19.9 g. of ZnO in 27.4 g. of KOH and stirring afteraddition of 52.7 g. of water.

It is desirable to add a soluble phosphate salt to the electrolyte. Asthe phosphate salt, potassium phosphate, especially potassiumpolyphosphate is preferred. As for the air cell, only the necessaryamount of atmospheric air for depolarization penetrates into the cellduring the discharge period, but atmospheric oxygen dilfuses from thecathode into the cell during storage and the anode, thereby, suifersfrom oxidative corrosion.

Consequently, the cell is self-consuming, and the cell can be storedonly short periods of time, e.g. within about a month, the cell will becompletely self-consumed. However when a phosphate salt is added to theelectrolyte, it adheres by surface active action on the surface of thezinc anode and forms a molecular film which protects the zinc, thereby,oxidative corrosion is prevented and the battery can be stored for longperiods of time, e.g., about 5 months.

When the amount of phosphate is over 3 percent of the electrolyte byweight, internal resistance of the cell increases, thereby dischargecharacteristic goes down. When it is less than 0.3 percent by weight, itis not elfective. Thus the range from 0.3 to 3 percent is elfected. Whenusing potassium polyphosphate, about 1 percent is suitable. For purposeof comparison, the characteristics at 50 ma.-continu0us discharge ofADZ-Z type air dry cell are shown in Table 1 in two cells, i.e. cell Awith 1 percent (by weight) of potassium polyphosphate based on thealkali zincate electrolyte and cell (a) without adding the same.

shell for 100 days (voltage) (in storage).

Instead of soluble phosphate, soluble silicate is also suitable. As thesoluble silicate, potassium silicate is generally used and the preferredamount is 0.33 percent of the electrolyte by weight.

Continuous discharge performance (terminal voltage V) at 50 ma. obtainedafter 100 days storage exposed in the air of cell (B) containing 1% (byweight) of potassium silicate per potassium zincate electrolyte, andcell (b) without adding the same in AD2 type air dry cell is shown inTable 2.

. TABLE 2 7 Discharge hours v0 10 20 30 70 B- Voltage, V 1. l2 1. 101.08 1.07 1 05 V 0 75 b do l. 13 0.81

In lieu of phosphate or silicate, a water-soluble compound having anacrylic radical e.g. polyacrylic acid, or potassium -or sodium saltpolyacrylic acid can also be employed as additive.

In contrast to the above-mentioned phosphate or silicate, thesecompounds make the deposition or segregation of oxide on the surface ofthe zinc anode so soft that the tendency of making the anode irnpassivecan be avoided, thereby improving the discharge effect. The preferredamount of compound is 1-3 percent by weight. Polymers of these types ofcompounds, especially polymers having a molecular weight of 50,000, arepreferable to the monomeric compounds. The characteristics (terminalvoltage V) of 400 ma.-continuous discharge at 20 C. in AWZ2-60 air wetcell are shown in the table where, in cell (C), 3 percent by weight ofsodium salt powder of polyacrylic acid (polymerization degree 50,000) isadded to the electrolyte of potassium zincate; in cell (C'), 3 percentof polyacrylic acid (polymerization degree 50,000) is added to theelectrolyte of potassium zincate; in cell (C'), 3 percent of polyacrylicacid (polymerization degree 50,000) is used instead of sodium salt ofpolyacrylic acid of cell (C); and in the cell (c), only potassiumzincate is used.

TABLE 3 Discharge hours (H) 0 100 200 300 400 500 C Voltage V 1. 10 1.12 1. 09 1. 11 1. 11 1. 02 O do 1.00 1.10 1.09 1.08 1.07 0.97 c d01.10 1. 13 1.11 0.98 0.83

TABLE 4 Discharge capacity D VoltageV 1.14 1. 14 1. 13 1. 10 1.08 Ddo 1. 11 1. 11 1. 08 1. 05 0. d do 1.13 1. 13 '1. 11 0. 98

In the case of an air dry cell, alkali zincate electrolyte which isabsorbed by cellulosic material like cotton and pulp or those made intopaste form by mixing with gelatinizing material to bring it intoimmobilized state, is used. For the purpose of gelatinizing,carboxy-methyl cellulose (polymerization degree 200-350) amounting to 11percent of alkali zincate by weight is preferably used. This materialdoes not decompose like starch and gelation by electrolyte and gives agel which does not separate from the electrolyte while in use. When thepolymerization degree of carboxymethyl cellulose is from 100 to 150, itmust be used in large amounts, which tends to lower, discharge capacityand discharge voltage. When the polymerization degree is from 500 to700, it decomposes into lower polymers, during storage, and thereforebadly af- 5 fects the preservation properties. The dischargecharacteristic of 50 ma.-continuous discharge at 20 C. in ADZ-Z type airdry cell are shown in the Table 5, Where the cell E employs electrolytelayer prepared by adding 11 per- 6 20 C. in the air wet cell of typeAWZ-2-60 wherein the electrolyte concentration is varied, are shown inFIG- URE 5. The relation between K ZnO concentration and volume is shownin FIGURE 6. FIGURE 7 indicates the cent by weight of sodium carboxymethyl cellulose 5 characteristic of 200 ma.-continuous discharge at 20C. (polymefllatlon degrae based on P when the compositions ofelectrolyte varies according to l followed y heatmg at lmdef agltatlonand Table 8 and are compared with conventional electrolyte. gelatmation,and the cell (e) employs electrolyte absorbed F 35 to 50 percent (byweight) is preferable, and 43 III Porous 1011011 Cellulosepercent (-byweight) K ZnO concentration gives favour- TABLE 10 able result.

Discharge capacity TABLE 7 N0 11(16) 1? 12 13(18) 14 19 20 E VoltageV1.15 1.12 1.12 1. 09 0. 90 e do 1.10 1. 07 1.07 1.05 1.00 15 K2ZI102Concentration"..- 39 43 60 TABLE 8 Composition--- 43% K2ZnO2 %7%116OH,100g. 88% K811, 75 g 88% KOH, 100 g. n, g

TABLE 6 Discharge capacity F... Voltage V 1. O8 0. 84 F "do 1. 12 1.10 1. 07 1. 04 0. 80 f do 1 02 1.01 0. "0

The characteristic of 100 mat-continuous discharge of A\VZ2type air wetcell at 20 C. which employs the electrolyte prepared by admixing variousamounts of 43 percent potassium hydroxide solution and various amountsof 43 percent K ZnO aqueous solution in their volumetric ratio is shownin FIGURE 3. It is clear that when using only 43 percent K ZnO thereinobtained a smooth discharge characteristic. In the case of ADZ-2 typeair dry cell at 20 ma.-continuous discharge (terminal voltage V) of 20C., a 43 percent aqueous solution of K ZnO gives a smooth dischargecharacteristic as shown in FIGURE 9.

These facts show that when a small amount of OH- exists which is formedfrom the hydrolysis of K ZnO aqueous solution at equilibrium, onlyEquation 2 occurs which gives a very smooth characteristic, but when theamount of OH- is more than that formed from the hydrolysis of K ZnO bothEquations 1 and 2 occur, which does not give smooth characteristicbecause of voltage drop at the transition point of the two reactions.

FIGURE 4 shows the relation between days of discharge duration andvolumetric ratio of admixing of 43 percent KOH aqueous solution and 43percent K ZnO aqueous solution in the AWZ-2-60 type of air wet cell whenit is intermittently discharged at room temperature by connecting 509resistance, followed by 56 minutes of stoppage. It is also clear thatusing only 43 percent K ZnO aqueous solution gives excellent results.

FIGURE 10 shoWs the case of ADZ-Z-type air dry cell wherein discharge isperformed intermittently at 8 ma. for 4 hours, followed by 20 hours ofstoppage. Also when using only a 43 percent K ZnO aqueous solution theresults are excellent.

The characteristics of 200 ma.-continuous discharge at Thecharacteristic of 20-ma.-continuous discharge at 20 C. and ADZ-2 typeair dry cell are shown in FIG- URE 11 when the concentration of theelectrolyte varies, according to Table 7, and the relation between K ZnOconcentration and volume are shown in FIGURE 12. The

characteristics of 20 ma.-continuous discharge at 20 C.

are shown in FIGURE 13 when the compositions are varied according toTable 8 and are compared with conventional electrolyte. As forconcentration of K ZnO it is clear that from 35 to 45 percent by weightis preferable; 43 percent being the most preferred.

The anode Porous zinc is used as the anode. The anode of this inventionhas a larger reaction surface area than conven tional cast or rolledzinc, and accordingly it can support a heavy load. Since the electrolyteof this air cell is an aqueous solution of alkali zincate, the anodesurface is covered by a dense film of zinc oxide produced in accordancewith Equation 2. This passivates the anode and the cell life ends,leaving only unreacted zinc when cast or rolled zinc is used. Howeverwhen porous zinc having a porosity of 30-70 percent is used the densefilm of zinc oxide is avoided and the passage of electric current is nothindered. In other words, a greater part of the zinc is utilized in theelectromotive reaction, thereby permit ting a current density 20 timeshigher. As the porosity of the porous zinc is in equilibrium with volumeincrease due to discharge reaction, there is no apparent volume increase(outside volume). Even when the anode is immersed in the electrolyte, asthe case of air wet cell, the fluctuation of liquid surface is slightand the electrolyte does not overflow from the cell. Even when the anodeis in contact with the electrolyte, it does not cause leakage ofelectrolyte by compressing the electrolyte layer.

The anodes are fabricated as follows. First, the anode of the air wetcell will be explained.

Around a 20 mesh grid net composed of, e.g., zincplated iron wire of 1mm. diameter, is fastened an iron frame, and 2050 mesh zinc powder iscompression molded by applying a pressure of 2000 1b./in. placing theabove-mentioned grid in the center, thereby giving better mechanicalstrength than when the zinc powder is simply compression molded. Inanother example, a tinplated 50 mesh grid is inserted into a pocket madeof porous glass cloth, zinc powder of -150 mesh is charged around thesame grid, and while the whole body thus obtained is immersed in aSOlUltlOn containing 1 percent corrosive sublimate, 12 percent mercury(by weight) is added dropwise, and left for 4 hours to obtain anamalgarn. In the thus obtained anode, mercury acts as a binder whichbinds the individual zinc particles and also the zinc particles to thegrid. The porosity of this cathode is 50-60 percent.

A mixture of 100 parts by weight of 50-100 mesh zinc powder (10 percentof which is amalgamated) and 3 parts by weight of 50 mesh polystyrene isheated at 150 C. for 2 hours. While the polystyrene is in the moltenstate, the whole mixture is subjected to compression molding, thereby ananode having a porosity of 50-60 percent is obtained. Also when zincpowder of 100-300 mesh is baked at 350-4l0 C. for 4 hours under anatmosphere of hydrogen flowing at the rate of 0.5-0.6 l. (1 atm.)/ cm.an anode of 60-70 porosity is obtained. Further when zinc powder of20-150 mesh is charged into the porous glass cloth pocket withoutapplying pressure, an extremely porous, valuable, anode, i.e.,non-compressingnon-molding anode, is obtained. Furthermore, when Zincpowder which is immersed in a solution of resin inert t alkali, e.g.,polyethylene or ethylcellulose, followed by evaporation of the solventresulting in formation of porous resin film on the surface, is employed,the self-consumption during storage due to oxidation of zinc is reduced, thereby increasing the length of time the battery can be stored.

Table 9 shows the characteritsics of 100 ma.-continuous discharge at 20C. in the air wet cell of type AWD- 2-60 wherein the cell (G) employs ananode which is made by charging 70 g. of a' mixture consisting of 100parts of 50-100 mesh zinc powder (10 percent of which is amalgamated)and 3 parts of 50 mesh polystyrene powder into a holding frame havingperforation of 2 mm. diameter, followed by heat-molding at 15 0 C. for 2hours; the cell (g) employs cast zinc, thecell (6') employs an anodemade by compression-molding the 50-100 mesh zinc powder into the holdingframe perforation of TABLE 9 Di'char e ca acit kminuiinn nun 0.1 10 20a0 40 50 (1---- Voltage v 1.11 1.11 1. 09 1.08 1. 07 1. g do 1.13 1.00 odo 1.00 1.08 1.04 o" "do 1.11 1.10 1.07 1. 05 1.0a G" -410 1.11 1.101.09 1.09 1.08 1.07

TABLE Discharge capacity (AH) 0 10 shown in Table 11.

TABLE 11 Although these anodes are made by compression molding, theybreak easily in the course of transportation or even in storage. Henceit is desirable to cover the surface with material which is insertedinto the electrolyte but permeable to ions, for example, a net made ofsodium carboxymethyl cellulose.

Next, a detailed description of the air dry cell anode is given.

By using a resin such as polyethylene oxide, polystyrene andethylcellulose as binder, zinc powder is molded.

For example, 5 g. of 100-150 mesh zinc powder are added to 0.5 g. of 5percent polyethylene oxide aqueous solution. When the mixture thusobtained is molded without applying pressure, there is obtained an anodeof 60 percent porosity. In another example, a mixture of 100 parts of50-100 mesh zinc-powder (10 percent amalgamated) and 3 parts of 50 meshpolystyrene powder is molded by heating for 2 hours at 15 0 C. It isalso possible to mix zinc powder with resin powder and mold withoutcompression by heating at a temperature higher than the softening pointof the same resin, the said resin being inert to the electrolyte, havingbinding properties and being gelatinisable when admixed with theelectrolyte like sodium carboxymethyl cellulose powder.

When 50 g. of 20-25 mesh zinc powder, 1 g. of 100 mesh polystyrenepowder and 2.5 g. of carboxymethyl cellulose are admixed, followed byheating at 150 C., there is obtained an anode of 55 percent porosity.

Similar to the case of the wet air cell, the anode is also made bybaking the zinc powder.

When the gel type electrolyte is employed, it is favorable to dispersezinc powder homogeneously. .This serves both as an anode and anelectrolyte, thereby the cell is small, light, has a smooth voltagecharacteristic, increased electricity capacity, and can be stored forlong periods of time.

Table 12 shows the characteristic of 50 ma.-continuous discharge(terminal voltage) at 20 C. in ADZ-Z-type air dry cell, where the cell(i) employs an anode made by casting 2 percent amalgamated zinc; thecell (I) employs an anode which is made by compression-molding 20-50mesh amalgamated zinc powder around a grid having perforations; the cell(I') employs an anode made by compression molding 20-50 mesh 10 percentamalgamated zinc powder; the cell (II") employs an anode made by dipping100 parts of 20-50 mesh 10 percent amalgamated zinc powder in 10 partsof 5 percent alcoholic solution of ethylcellulose, followed by dryingunder vacuum; the cell (1") employs an anode made by charging 20-50 mesh10 percent amalgamated zinc powder into the cell case and placing theelectrolyte layer upon this; and the cell (I") employs an anode made byheating a mixture comprising 100 parts of 10 percent amalgamated zincpowder (20-50 mesh) and 3 parts of 50 mesh polystyrene powder at atemperature of 150 C. for 2 hours, followed by molding.

TABLE 12 Discharge volume AH 0 1 2 3 4 Table 13 shows the characteristicof 50 ma.-continu0us discharge at 20 C. (terminal voltage V) inADZ-2-type air dry cell, where the cell (J) employs an anode made bybaking -150 mesh zinc powder at 350 C.; and the cell (j) employs ananode made by compression molding 100-150 mesh zinc powder.

TABLE 13 Capacity (AH) 0 1 2 3 4 9 10 It is efiective to use zincpowder, the surface of which Instead of the above-mentioned cylinder, itis also is coated with porous resin. desirable to fill the vacant spacebetween the anode- Next, the anode, which is also the electrolyte, willbe electrolyte and the anode terminal with metal fiber cloth explainedin detail. or plastic sponge which is resistant to the electrolyte, e.g.

When the ratio of the electrolyte to zinc powder is neoprene sponge.from 4.5 :5 .5 to 3 :7 (by weight), there is no oxidative cor- Thecathode rosion because each particle of zinc powder is in electricalcontact with each other because they are surrounded by the electrolyte.Furthermore, with this ratio, discharge capacity is high and voltagecharacteristic is smooth, therefore it is the most favorable range. Whenthe ratio is greater than aforementioned, internal resistance anddischarge capacity decreases, in spite of an increase of load voltage.Moreover, storage performance is poor because the. surface of zincpowder is not separated from oxygen in air by the electrolyte. When theratio is smaller, internal resistance increases and both dischargevoltage and capacity is poor.

For the anode-electrolyte, it is favorable to homogeneously mix 0.4 partof sodium carboxymethyl cellulose, having a polymerization degree of200350, 3.6 parts of 43 percent alkali zincate aqueous solution and 6parts of l00-l50 mesh zinc powder, 10 percent of which is amal- As thecathode, an active carbon electrode is used. In the air dry cell, thecathode absorbs oxygen in the air and acts as a depolarizer, the activecarbon electrode must be porous so as to be air penetrable and also bewaterproof to prevent leakage of the electrolyte.

The active carbon cathode, as aforementioned, acts as a depolarizer byabsorbing oxygen in the air. In addition it is also an exhauster bymaking the gas pass through pores when the internal pressure of the cellis increased by the gas produced in the cell or by volume increase dueto the discharge reaction. Leakage of the electrolyte is thus avoided.

One example of an active carbon cathode is as follows: 20 g. of activecarbon mixed with a binder composed of g. of polystyrene dissolved in150 cc. benzene is compression molded. Thereafter the benzene isevaporated. gamated As another example, a mixture of 10 parts ofcharcoal In Table 14 preservation characteristics of several kinds 25 P3 Paris of morgamc actlvator and 4 Parts a of ADZ 2 type air dry cellare given Where the cells K, binder (tar pitch) 1s molded, baked andtreated with K, K" employ an anode-electrolyte, formed of 43 percentParaffin to make 1t water'proofalkali zincate electrolyte gelatinized bysodium carboxythe Smface whfch In Contact methyl cellulose ofpolymerization degree 200 to 350 and the electrode, and is participatingin the electromotive 100 m 150 mfish amalgamated Zinc containing 10percent reaction, an ion-permeable separator is placed in order to ofmercury, the ratio being varied according to Table 14; isolate thedeposit Produced y the reaction fr m the d h 11 (1;) employs a layer f43 percent alkali anode For this purpose glass fiber cloth or vinyloncloth zincate gelatinized by sodium carboxymethyl cellulose and 1Sutlllzedporous zinc which is made by compression molding 100 The C611COHStIUCtlOH to 150 mesh amalgamated zinc powder containing 10 per- Theconstruction of typ air Wet Cell is Cent merC 'yshown in FIG. 1 and FIG.2. In the drawing, 1 is a poly- TABLE 14 styrene cell divided into twoparts, 2 is a cell cover, 3 is an active carbon cathode, 4 is a porouszinc anode, 5 is a Ratio mixing (weight) stopper inserted in a hole 6provided in the cell cover 2, 7

Electrolyte Zine powder is.a vent hole in the stopper 5, 8 is an oblongair hole 5 5 on the cell cover 2, 9 is a cathode terminal, 10 is an 3.52 anode terminal, 11 is 43 percent alkali zincate electrolyte,

12 is a grid having perforated holes 13, 14 is the porous TABLE 15Sample Voltage Appearance Voltage Appearance Voltage Appearance VoltageAppearance 1. 30 N orrnal 1.32 1.35 1.29 Normal 1.32 do 1. 26 Do. 1. 30-.do 1. 30 1.13 Starting to leak. 1. 24 Starting to 1.31 do 1.28 ..do

leak.

When the anode-electrolyte is used, the volume of zinc zinc layer, and15 is the separator covering the surface of cathode expands during thedischarge period, accordingthe anode 3. 1y some vacant area isnecessary. However if the electro- The anode and the cathode arearranged in diagonal lyte enters the Vacant because of expanslon of therelation to one another in the two parts of the cell and z p the Contactbetween the electrolyte layer and are connected in series. If thesurface of the grid, 12 is the cathode terminal or the contact betweenthe electrolyte i d by resin solution which i d by dispersing i layerand the diaphragm becomes P even by shght Shak powder in epoxy resin,the self-consumption of the cathing, which causes an increase ininternal resistance. If the anode-electrolyte is placed in an insulatingmaterial which is inert to the electrolyte, e.g. a netting cylinder madeof polyvinylidene chloride, the bottom of this cylinder is so placed asto be in contact with the diaphragm of the carbon cathode, while thecylinder top is in contact with the ode and internal gas evolution areavoided.

The construction of ADZ2 type air dry cell is shown in FIG. 8. In thedrawing, 16 is a nickel-plated steel case having an air hole 17, 18 is anickel-plated steel case having an air hole 19 which is connected withthe air hole anode terminal which is also serving as sealing plate, the20 is an active carbon Cathode, 21 is a sepafamr, 22 expansion pressureof the zinc powder caused by discharge is a 43 PermIlt alkali Zillcatcelectrolyte layer which is is dissipated through the net, and therefore,does not cause immobilized by gelatinizing agent, 23 is a porous zincany pressure and, in addition, leads to a balanced internal anode, 24 isa sealing plate made of tin-plated steel and resistance. 25 is a packingfor insulating the seal plate.

What is claimed is: I 1. Air cell comprising a cathode, an electrolyte,and an anode which generate the following electromotive reaction:

Zn+H 0+O -Zn(OH) ZnO-}-H O said cathode comprising active carbon, shapedby a binder, and having an ion-permeable separator on the surfacethereof which is in contact with the electrolyte, the anode comprisingporous zinc having from 30 to 70 percent porosity, and said electrolytecomprising 35' to 45 percent alkali zincate aqueous solution, said anodebeing in contact with said electrolyte.

2. Air cell as claimed in claim 1 wherein the ion per meable separatoron the surface of the cathode is selected 7 from the group consisting ofglass-fiber cloth and polyvinyl alcohol fiber cloth.

3. Air cell as claimed in claim 1, wherein the electrolyte containssoluble salt of phosphate in an amount of 0.3-3 percent by weight ofsaid electrolyte.

4. Air cell as claimed in claim 1, wherein the electrolyte containspotassium polyphosphate in an amount of 1 percent by weight of saidelectrolyte.

5. Air cell as claimed in claim 1 wherein the electrolyte contains from0.3 to 3 percent of soluble silicate based on the weight of theelectrolyte.

v 6. Air cell as claimed in claim 1 wherein the electrolyte contains awater-soluble acrylic compound in an amount of 1 3 percent based on theelectrolyte.

7. Air cell as claimed in claim 6 wherein the watersoluble acryliccompound is a polymer having a polymerization degree of about 50,000. Y

8. Air dry cell as claimed in claim 1 wherein carboxymethyl cellulosehaving a polymerization degree of 200 to 350 is employed as agelatinizing material in an amount of about 11 percent, therebyrendering the electrolyte immobile. i

References Cited UNITED STATES PATENTS 7/1907 Edison 136-157 2,422,04510/1947 Ruben 136107 2,526,692 10/1950 Ruben 136--107 2,612,532 9/1952Heise et al. 13686 2,650,945 9/1953 Herbert 136-107 2,800,520 7/ 1957McGraw 136154 X 2,848,525 8/1958 Schumacher etal. 136l02 2,941,9096/1950 Johnson et al. 136-154 a FOREIGN PATENTS 148,397 9/ 1952Australia.

ALLEN B. CURTIS, Primary Examiner.

1. AIR CELL COMPRISING A CATHODE, AN ELECTROLYTE, AND AN ANODE WHICHGENERATE THE FOLLOWING ELECTROMOTIVE REACTION: